1. Field of the Invention
The present invention relates to power circuit interruption and, more particularly, to fused circuit interruption of low voltage power busses.
2. Background Information
Copper Z, copper Y and S fuse links are designed to handle relatively high currents (e.g., about 800 A to about 6 kVA) and low voltage (e.g., up to about 600 VACRMS). The interrupting mechanism for the fuses (e.g., copper Z; copper Y) is the heat generated by passing fault level currents through a relatively small cross-sectional area of the fuse. The short period of time of elevated current does not allow sufficient time for the heat generated by the elevated current to dissipate throughout the fuse mountings. Eventually, the fuse will melt enough to create a gap in the fuse. The voltage will create an arc between the opposite ends of the gap, and the arcing will continue until the arc evaporates enough material, in order that the gap is extended enough distance that the arc can no longer be supported and is, thus, extinguished.
A network protector is a circuit breaker adapted to trip and open a feeder upon detection of reverse power flow (i.e., that is, power flowing through the feeder out of a network rather than into the network). Typically, overcurrent protection is provided by other devices, such as fuses, in series with the network protector. See, for example, U.S. Pat. Nos. 6,407,897; and 6,459,554.
U.S. Pat. No. 4,002,864 discloses a network protector including a drawout unit supported by a main support frame at ground potential. The drawout unit may be fully rolled out on extension rails of side plates of the main support frame. In that position, the drawout unit is completely disengaged from any source of high potential. A removable steel protective barrier covers the upper part of the drawout unit between the side plates. The protective barrier comprises a pair of handles, three quarter-turn fasteners mounted upon a flat steel plate and three glass polyester baffles. When the drawout unit is in the connected position, the baffles seat against flanges of the network protector enclosure, in order to contain any arcing products produced by operation of the network protector.
When a fuse or a plurality of fuses are employed in an enclosure (e.g., an enclosure for a network protector), the entire time that the arc is sustained, some metallic materials are vaporized, and other relatively larger, molten pieces of the fuse are thrown throughout the enclosure, thereby causing extensive damage to the protective barriers, and leaving a carbon and metallic dust over all components enclosed with the fuses. The length of time that the arc is sustained is the time that the fault is allowed to continue, thereby increasing potential damage to the equipment that the fuses are designed to protect.
There is room for improvement in power circuits employing fuses.